Ecoscenarios Combined - FOSSweb

Ecoscenario: Saguaro National Park
4/16/03 3:23 PM
Art Explosion
Humans are dwarfed by giant saguaro
cactus.
Courtesy of Anne Marie Gearhart
Thorns grow along the pleats of a
saguaro cactus.
During the rainy season, saguaros absorb huge amounts of water. Their accordian shape expands to hold more
water, and a thick, waxy epidermis slows transpiration.
Mixed with the saguaros are mesquite trees, ocotillo, creosote bushes, barrel cactus, prickly pear, and grama
grass. Each has its own adaptation for collecting and storing water. Cacti photosynthesize with the epidermis layer
of their stems. Thorns are leaves that have shrunk over time. The thorns also protect cacti by discouraging animals
from browsing on their water-rich tissues.
Some long-lived plants, such as mesquite trees and creosote bushes, have exceptionally long roots to reach water
deep in the earth. Other plants, including prickly pear and saguaro cactus, have shallow, netlike roots to help
capture water from the brief rains.
Soils in the desert are generally poor. In many places the ground is covered with a thin rocky layer called desert
pavement. It is a layer of pebbles and small rocks. All the surrounding sand has been blown or washed away,
leaving a surface that looks as if it was placed there on purpose. Desert pavement may take thousands of years to
form. Directly beneath the layer of pebbles is a thin layer of soil that contains organic material. This layer is rich in
cyanobacteria (blue-green algae), and may support substantial growths of algae, lichens, and mosses.
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